An organic light-emitting diode (OLED) on a carrier includes an organic functional layer structure between a first electrode and a second electrode, in which case the first electrode is in contact with the carrier and an encapsulation layer may be deposited on or over the second electrode. A flow of current between the electrodes leads to the generation of electromagnetic radiation in the organic functional layer system. Without technical assistance, normally only ˜20% of the electromagnetic radiation can be extracted from the OLED by means of total internal reflection inside the component.
The total internal reflection in the OLED can be reduced by the use of scattering layers, for example with a scattering layer between the first electrode and the carrier. In this way, a larger proportion of the electromagnetic radiation generated, for example light, can be extracted.
In a conventional scattering layer, an organic matrix is used in which scattering centers with a different refractive index are embedded (WO 02/37580 A1). Upon contact with water and/or oxygen, however, organic scattering layers can age or degrade and thus reduce the stability of an OLED. Another disadvantage of organic scattering layers is their low refractive index (n˜1.475). Since the organic functional layer structure usually has a refractive index of approximately 1.7, the low refractive index of the organic scattering layers entails moderate angles of incidence for the criterion of total internal reflection at the interface of the first electrode with the scattering layer.
Furthermore, scattering layers made of high-index glass solder with embedded scattering centers are conventional. The number density of the scattering centers conventionally decreases from the inside outward (EP 2 178 343 A1, US 2010/0187987 A1, WO 2011/046190 A1) or is homogeneous in the layer cross section. This layer cross section results from the conventional method for producing the layers, which are formed from a suspension, or a paste, of scattering centers and matrix substance, for example glass solder. The roughness of the scattering layer, or the shape of the scattering centers, may however lead to the formation of spikes on the scattering layer surface. When using scattering particles as scattering centers, scattering particles not fully enclosed by glass on the scattering layer surface may likewise form spikes. Spikes are to be understood as local surface roughenings with a high aspect ratio. Particularly in the case of a thin configuration of an OLED, spikes can lead to short circuiting of the first electrode with the second electrode. Furthermore, local distortion or decomposition of the layers on or over the scattering layer, for example the first electrode or the organically functional layer, may occur in the immediate vicinity of the spikes of the scattering layer during production of the OLED. If a thin-film encapsulation is applied on the component, then the spikes entail the risk that the thin-film encapsulation will not be locally dense, which can lead to degradation of the component.
The surface properties, for example a low surface roughness or a defined waviness, are conventionally adjusted by means of an additionally applied glass layer (EP 2 278 852 A1, WO 2010/084922, WO 2010/084923). This also reduces the risk that scattering particles not fully enclosed by glass will be present on the scattering layer surface. However, the additional layer usually requires an additional heat-treatment step and therefore lengthens the processing.